2,544 research outputs found
The Future of Particle Physics
After a very brief review of twentieth century elementary particle physics,
prospects for the next century are discussed. First and most important are
technological limits of opportunities; next, the future experimental program,
and finally the status of the theory, in particular its limitations as well as
its opportunities.Comment: Invited talk given at the International Conference on Fundamental
Sciences: Mathematics and Theoretical Physics, Singapore, 13-17 March 200
Quantum power correction to the Newton law
We have found the graviton contribution to the one-loop quantum correction to
the Newton law. This correction results in interaction decreasing with distance
as 1/r^3 and is dominated numerically by the graviton contribution. The
previous calculations of this contribution to the discussed effect are
demonstrated to be incorrect.Comment: 10 pages, 5 figures; numerical error corrected, few references adde
A Universe Without Weak Interactions
A universe without weak interactions is constructed that undergoes big-bang
nucleosynthesis, matter domination, structure formation, and star formation.
The stars in this universe are able to burn for billions of years, synthesize
elements up to iron, and undergo supernova explosions, dispersing heavy
elements into the interstellar medium. These definitive claims are supported by
a detailed analysis where this hypothetical "Weakless Universe" is matched to
our Universe by simultaneously adjusting Standard Model and cosmological
parameters. For instance, chemistry and nuclear physics are essentially
unchanged. The apparent habitability of the Weakless Universe suggests that the
anthropic principle does not determine the scale of electroweak breaking, or
even require that it be smaller than the Planck scale, so long as technically
natural parameters may be suitably adjusted. Whether the multi-parameter
adjustment is realized or probable is dependent on the ultraviolet completion,
such as the string landscape. Considering a similar analysis for the
cosmological constant, however, we argue that no adjustments of other
parameters are able to allow the cosmological constant to raise up even
remotely close to the Planck scale while obtaining macroscopic structure. The
fine-tuning problems associated with the electroweak breaking scale and the
cosmological constant therefore appear to be qualitatively different from the
perspective of obtaining a habitable universe.Comment: 27 pages; 4 figure
Fermion masses in noncommutative geometry
Recent indications of neutrino oscillations raise the question of the
possibility of incorporating massive neutrinos in the formulation of the
Standard Model (SM) within noncommutative geometry (NCG). We find that the NCG
requirement of Poincare duality constrains the numbers of massless quarks and
neutrinos to be unequal unless new fermions are introduced. Possible scenarios
in which this constraint is satisfied are discussed.Comment: 4 pages, REVTeX; typos are corrected in (19), "Possible Solutions"
and "Conclusion" are modified; additional calculational details are included;
references are update
The anthropic principle and the mass scale of the Standard Model
In theories in which different regions of the universe can have different
values of the the physical parameters, we would naturally find ourselves in a
region which has parameters favorable for life. We explore the range of
anthropically allowed values of the mass parameter in the Higgs potential,
. For , the requirement that complex elements be formed
suggests that the Higgs vacuum expectation value must have a magnitude less
than 5 times its observed value. For , baryon stability requires that
, the Planck Mass. Smaller values of may or may not be
allowed depending on issues of element synthesis and stellar evolution. We
conclude that the observed value of is reasonably typical of the
anthropically allowed range, and that anthropic arguments provide a plausible
explanation for the closeness of the QCD scale and the weak scale.Comment: 28 pages, LaTeX. No changes from version originally submitted to
archive, except that problem with figure file has been correcte
Photon-Photon Scattering, Pion Polarizability and Chiral Symmetry
Recent attempts to detect the pion polarizability via analysis of
measurements are examined. The connection
between calculations based on dispersion relations and on chiral perturbation
theory is established by matching the low energy chiral amplitude with that
given by a full dispersive treatment. Using the values for the polarizability
required by chiral symmetry, predicted and experimental cross sections are
shown to be in agreement.Comment: 21 pages(+10 figures available on request), LATEX, UMHEP-38
Effective Gravitational Field of Black Holes
The problem of interpretation of the \hbar^0-order part of radiative
corrections to the effective gravitational field is considered. It is shown
that variations of the Feynman parameter in gauge conditions fixing the general
covariance are equivalent to spacetime diffeomorphisms. This result is proved
for arbitrary gauge conditions at the one-loop order. It implies that the
gravitational radiative corrections of the order \hbar^0 to the spacetime
metric can be physically interpreted in a purely classical manner. As an
example, the effective gravitational field of a black hole is calculated in the
first post-Newtonian approximation, and the secular precession of a test
particle orbit in this field is determined.Comment: 8 pages, LaTeX, 1 eps figure. Proof of the theorem and typos
correcte
Casimir bag energy in the stochastic approximation to the pure QCD vacuum
We study the Casimir contribution to the bag energy coming from gluon field
fluctuations, within the context of the stochastic vacuum model (SVM) of pure
QCD. After formulating the problem in terms of the generating functional of
field strength cumulants, we argue that the resulting predictions about the
Casimir energy are compatible with the phenomenologically required bag energy
term.Comment: 16 page
Final state rescattering as a contribution to
We provide a new estimate of the long-distance component to the radiative
transition . Our mechanism involves the soft-scattering of
on-shell hadronic products of nonleptonic decay, as in the chain . We employ a phenomenological fit to scattering data
to estimate the effect. The specific intermediate states considered here modify
the decay rate at roughly the level, although
the underlying effect has the potential to be larger. Contrary to other
mechanisms of long distance physics which have been discussed in the
literature, this yields a non-negligible modification of the channel and hence will provide an uncertainty in the extraction of
. This mechanism also affects the isospin relation between the rates
for and and may generate CP
asymmetries at experimentally observable levels.Comment: 15 pages, RevTex, 3 figure
- …